Add missing urls for Box doc

src/liballoc/boxed.rs

@@ -244,12 +244,14 @@ impl<T: ?Sized> Box<T> {
     /// the destructor of `T` and free the allocated memory. Since the
     /// way `Box` allocates and releases memory is unspecified, the
     /// only valid pointer to pass to this function is the one taken
-    /// from another `Box` via the `Box::into_raw` function.
+    /// from another `Box` via the [`Box::into_raw`] function.
     ///
     /// This function is unsafe because improper use may lead to
     /// memory problems. For example, a double-free may occur if the
     /// function is called twice on the same raw pointer.
     ///
+    /// [`Box::into_raw`]: struct.Box.html#method.into_raw
+    ///
     /// # Examples
     ///
     /// ```
@@ -269,12 +271,14 @@ impl<T: ?Sized> Box<T> {
     /// memory previously managed by the `Box`. In particular, the
     /// caller should properly destroy `T` and release the memory. The
     /// proper way to do so is to convert the raw pointer back into a
-    /// `Box` with the `Box::from_raw` function.
+    /// `Box` with the [`Box::from_raw`] function.
     ///
     /// Note: this is an associated function, which means that you have
     /// to call it as `Box::into_raw(b)` instead of `b.into_raw()`. This
     /// is so that there is no conflict with a method on the inner type.
     ///
+    /// [`Box::from_raw`]: struct.Box.html#method.from_raw
+    ///
     /// # Examples
     ///
     /// ```